Ø  Cement and Concrete- Aren’t they the exact same thing?

          Definitely not. Though these two words are sometimes used referring to the same thing (i.e. cement pavement), they are not the same thing. Concrete is an end product made up of sand, rock, and the component that glues it together is Portland Cement.

Ø  How strong is concrete?

                 Concrete is one of the most durable and versatile materials we know of. Through a process called “hydration”, concrete transforms from a malleable plastic substance into a hardened tough material. The concrete continues to harden for years after it is set in place, making it even stronger over time.

Ø  How do I cure concrete?

                 To greatly impact both the longevity and strength of concrete that one should “cure” the concrete. Curing is a very important step in the concrete process. As we mentioned earlier, concrete hardens as a result of hydration when the water and chemicals in the concrete are able to interact and essentially fuse together. However, if water is not available to the concrete, hydration cannot occur. This is where curing comes into action. The process involves keeping the concrete moist over about a week period to allow the hydration process to occur. The curing process should begin immediately after final finishing.

Here are some curing methods that are popular to keep the concrete moist. If you use a curing compound as your method of choice, please remember that with colored concrete, it may require a curing compound that is approved for application with colored concrete.

v  Concrete soaking hoses

v  Sprinklers

v  Wet burlap sacks placed over the concrete

v  Curing compounds that seal in the moisture

Remember temperature plays a significant role in this process as well. If it’s too hot the moisture will evaporate and conversely if it’s too cold the process may not happen at all. A good rule of thumb to follow is to cure in temperatures above 52 degrees Fahrenheit.

Ø  What are Concrete mix proportions?

                  Concrete mix proportions are the amount of cement, water, air and aggregates are used to create a final concrete product. Generally, to create strong quality concrete result, the “rule of six” is a strong method to follow. This rule states to use six bags of cement for every cubic yard of concrete needed, six gallons of water per bag of cement, a six day curing period, and an air content of six percent.

        Ø  How can I avoid concrete cracks?

                   There are many different types of concrete cracks. Proper joint layout is critical in flatwork. Pouring concrete with a low-slump is also very important. Cracks can also be caused from external restraint. (Pouring a footing and slab concurrently) Cracks can occur in between two immovable obstructions. If felt or foam is not used between a house and a block wall it is likely that a crack will develop. Crazing cracks (web cracking) often will develop when concrete is poured with a high slump and/or bleed water or water was introduced to the surface of the drying concrete before final set.

Ø  Why is my concrete cracking?

                  Concrete, like any material, is directly affected by temperature and changes in volume. In the beginning stages, concrete will shrink in volume slightly as it dries causing cracks to occur. Later sharp changes in temperature can cause the cracks to start or existing cracks to become larger.

A way to cope with this draw back is to follow the methods of concrete contractors and put joints in the concrete pavement. This won’t stop the cracking but it will allow the cracks to occur in neat straight lines at the joint when concrete begins to shrink.

Ø  How far apart should I place my contraction joints?

                  The recommendations are that you place your contraction joints no more than 2 times in feet the thickness in inches of the slab. (4” slab 8’ joint spacing) These joints must be a minimum of ¼ the depth of the slab. (1” on 4” slab) Also, it is recommended that you attempt to design panels that are as square as possible.

Ø  Should I use fibers in my concrete?

                  We recommend the use of fibermesh for reducing the possibility of plastic shrinkage cracks. But point out that fibermesh does not replace the use of wire mesh or rebar.

Ø  How should I prepare my sub-grade?

                  The sub-grade should be well compacted, uniform in depth, and well draining. Also, a fill of granular nature such as sand, rock or crushed base and dampen this base before placing concrete.

Ø  How should I prepare for cold weather?

                   We recommend that when the mercury drops you should use a set accelerator in your mixes along with hot water. Accelerators: Calcium, this can not be used in colored loads, and “POZZ” a Non-Corrosive accelerator. Also, pouring your concrete with a low slump will help increase your set times.

  Ø  How should I prepare for hot weather?

                   Concrete will set-up much quicker in hot weather. Ask our order takers to add a set retarder to your load. Make sure you have enough people on site to place the concrete quickly. It is recommended that the sub-grade is dampened before placement begins.

Ø  What do I need to know about colored concrete?

                   Extra care must be taken when placing colored concrete. It is important that the slump remains consistent throughout each load. Also, as with any concrete, you never want to introduce water to the drying surface.

Ø  How do I avoid discoloration of my slab?

                   It is important not to over use a steel trowel while finishing. This has an effect that “burns” the surface of the concrete and seals in moisture. (Trapped) Also, you do not want to introduce any steel onto the wet concrete until after all of the bleed water has disappeared. Avoid using calcium chloride (Accelerator) for flatwork.

Ø  How can I repair discoloration?

                   Discoloration is difficult to fix. However, the earlier you treat the surface the more effective it will be. Scrub white vinegar onto the dampened slab and hose off the surface before the vinegar dries. Vinegar is slightly acidic and will often open up the pores of the concrete and allow it to breath. Discoloration caused by calcium chloride will not be affected by this procedure.

Ø  What Is Pervious Concrete?

                   Pervious concrete is concrete manufactured with zero fine aggregate. It allows water to pass through the concrete which eliminates storm water run-off. Pervious concrete pavement is a unique and effective means to address important environmental issues and support sustainable growth. By capturing stormwater and allowing it to seep into the ground, porous concrete is instrumental in recharging groundwater, reducing stormwater runoff, and meeting EPA stormwater regulations.

Ø  How do I know that the concrete I paid for is the concrete I’m receiving?

                   After figuring out exactly what type of concrete you need, it is easy to trust that your dealer will supply what you want. You can always perform a concrete test to confirm the type of concrete being used. There are many test that apply to different types of concrete. Here are a few:

v  Slump Test- Slump is simply the consistency of the concrete. The relative ability of the concrete to flow when being put in place is very important and problems can arise if the slump level is too low, such as proper consolidation of the concrete. Likewise if the slump is too high, meaning if there is too much flow in the concrete there can be several issues including finishing delays and segregation.

v  Air Content Test- This test is executed by taking some fresh concrete and measuring the total air content contained within it. This test however, is not entirely accurate because some air will eventually be lost in transportation, consolidation, etc.

v  Unit Weight Test- Weight of a known volume of fresh concrete is a fairly good indication of the makeup contained within it.

v  Compressive Strength Test- Measuring the force needed to break concrete goes through its hardening process and is executed at pre set intervals.

       Ø  What is “three thousand pound” concrete?

                                Three thousand pound concrete has stress strength of 3000 psi. This has to be maintained over a 28 day period. It isn’t the only strength out there but it is very common for most concrete to have less than a 7000 psi.

Here are a few brief tips about ordering concrete in case the above didn’t help:

ü  Always carefully measure length, width and depth of the area that you need to fill.

ü  Be sure that the area of placement is graded accordingly and evenly for an accurate measurement.

ü  Make sure there is a clear path to your job site and that there will be no delays after the truck arrives. You don’t want to have the concrete driver wait around because the concrete is best used when it is as fresh as possible.